This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-334796, filed on Nov. 19, 2002, the entire contents of which are incorporated herein by reference.
The present invention relates to a torque detector used for adding an assisting force generated by a motor to an automobile steering system and to an electric power steering controller provided with a torque detector.
Heretofore, there have been various proposals of torque detectors for detecting the steering torque of a steering system and controlling the drive current of an electric motor in accordance with the steering torque so as to add an assisting force to the steering torque. There have also been various proposals of electric power steering apparatuses provided with torque detectors.
In conventional torque detectors and electric power steering apparatuses, the steering force applied by a driver is detected, and the detected steering force is subjected to A/D conversion and input to a microcomputer. The microcomputer carries out an arithmetic operation on the input value for performing assist control to calculate an output value. Then, the microcomputer applies an assisting force with a motor to the automobile steering system in accordance with the output value.
The A/D conversion results in truncation errors and computational errors. Thus, even though the actual input value is constant, the output value of the computation result may fluctuate and produce abnormal noise or adversely affecting steering sensation.
A conventional electric power steering apparatus that suppresses fluctuation of input value information generally has a microcomputer to perform an averaging filter process and average the input values, as shown in the flow chart of FIG. 1. In FIG. 1, the microcomputer first receives a signal corresponding to the steering torque in step S101 and calculates the steering torque in accordance with the received signal (step S102).
In step S103, the microcomputer determines whether or not the calculated steering torque is a value that has initially been obtained after starting the execution of a control program. When the steering torque is an initial value, the microcomputer proceeds to step S104 and sets the steering torque as the output value. When determining that the calculated steering torque is not an initial value, the microcomputer proceeds to step S106 to perform an averaging filter process on the steering torque. The value obtained through the averaging filter process is set as the output value.
In the averaging filter process, the present steering torque value is added to a plurality of steering torque values (data) obtained in the past. Then, the sum of steering torque values is averaged. In step S105, the present output value obtained in step S104 or step S106 is stored as a past output value in a memory device, such as a RAM. Then, the control program is temporarily ended.
In addition to the process of FIG. 1, a further filter process may be executed a number of times. A median filter process may also be executed. Therefore, in the prior art, fluctuation of the input values is suppressed in the data value. However, in the prior art, there is a shortcoming in that the response to sudden changes of the input value is not satisfactory.
One aspect of the present invention is a torque detector for detecting torque that is produced when a steering shaft of a vehicle is rotated. The torque detector includes a detection element for detecting steering torque that is applied to the steering shaft when the steering shaft is rotated to generate an analog torque signal corresponding to the steering torque. A converter is connected to the detection element to convert the analog torque signal to a digital torque signal. A hysteresis processor is connected to the converter to perform hysteresis processing on the digital torque signal so that a value of the digital torque signal is included in a predetermined range.
Another aspect of the present invention is a torque detector for detecting torque that is produced when a steering shaft of a vehicle is rotated. The torque detector includes a detection element for detecting steering torque that is applied to the steering shaft when the steering shaft is rotated to generate an analog torque signal corresponding to the steering torque. A converter is connected to the detection element to convert the analog torque signal to a digital torque signal. A calculation unit is connected to the converter to continuously receive the digital torque signal from the converter and perform a predetermined calculation process on the digital torque signal. The calculation unit includes an averaging processor connected to the converter to perform averaging processing on at least one value of the digital torque signal received in the past and the value of the currently received digital torque signal. A determiner determines the relationship between a predetermined threshold value and the value of the digital torque signal averaged by the averaging processor. A hysteresis processor performs hysteresis processing on the currently received digital torque signal to include the currently received digital torque signal in a predetermined range when the determiner determines that the value of the averaged digital torque signal is greater than the predetermined threshold value.
A further aspect of the present invention is an electric power steering controller for assisting operation of a vehicle steering device, the steering device including a steering shaft connected to a steering wheel. The electric power steering controller includes a torque detector for detecting torque that is produced when the steering shaft is rotated. The torque detector includes a detection element for detecting steering torque that is applied to the steering shaft when the steering shaft is rotated to generate an analog torque signal corresponding to the steering torque. A converter is connected to the detection element to convert the analog torque signal to a digital torque signal. A hysteresis processor is connected to the converter to perform hysteresis processing on the digital torque signal so that a value of the digital torque signal is included in a predetermined range. An electric motor is connected to the torque detector to generate motor torque that is added to the steering force of the steering shaft. A motor controller is connected to the torque detector and the electric motor for obtaining the motor torque corresponding to a digital torque signal subjected to the hysteresis processing and controlling the motor.
A further aspect of the present invention is an electric power steering controller for assisting operation of a vehicle steering device. The steering device includes a steering shaft connected to a steering wheel. The electric power steering controller includes a torque detector for detecting torque that is produced when the steering shaft is rotated. The torque detector includes a detection element for detecting steering torque that is applied to the steering shaft when the steering shaft is rotated to generate an analog torque signal corresponding to the steering torque. A converter is connected to the detection element to convert the analog torque signal to a digital torque signal. A calculation unit is connected to the converter to continuously receive the digital torque signal from the converter and perform a predetermined calculation process on the digital torque signal. The calculation unit includes an averaging processor connected to the converter to perform averaging processing on at least one value of the digital torque signal received in the past and the value of the currently received digital torque signal. A determiner determines the relationship between a predetermined threshold value and the value of the digital torque signal averaged by the averaging processor. A hysteresis processor performs hysteresis processing on the currently received digital torque signal to include the currently received digital torque signal in a predetermined range when the determiner determines that the value of the averaged digital torque signal is greater than the predetermined threshold value. An electric motor is connected to the torque detector to generate motor torque that is added to the steering force of the steering shaft. A motor controller is connected to the torque detector and the electric motor for obtaining the motor torque of the electric motor. The motor controller obtains the motor torque corresponding to the digital torque signal subjected to the hysteresis processing when the determiner determines that the averaged value of the digital torque signal is greater than the threshold value. The motor controller obtains the motor torque corresponding to the averaged value of the digital torque signal when the determiner determines that the average value of the digital torque signal is less than or equal to the threshold value.
A further aspect of the present invention is a torque detector for detecting torque that is produced when a shaft is rotated. The torque detector includes a detection element for detecting the torque that is applied to the shaft when the shaft is rotated to generate a torque signal corresponding to the torque. A calculation unit is connected to the detection element to perform hysteresis processing on the torque signal so that a value of the torque signal is included in a predetermined range.
A further aspect of the present invention is a method for detecting torque that is produced when a shaft is rotated. The method includes detecting the torque applied to the shaft when the shaft is rotated, generating a torque signal corresponding to the detected torque, and performing hysteresis processing on the torque signal to include the value of the torque signal in a predetermined range.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.